Imaging Techniques
Plain film X-ray: Plain film radiography is often used as first-line imaging to demonstrate a lymphatic leak. Chest x-ray often demonstrates a pleural effusion and abdominal x-ray may suggest the presence of peritoneal fluid.
Ultrasound: Ultrasonography is particularly sensitive for detecting the presence and quantity of fluid. Ultrasonography can demonstrate dilation of intestinal loops, diffuse thickening of walls and mesenteric edema. Sonographic evaluations are limited in the setting of obesity or complex multiloculated ascites.
Computed Tomography (CT): CT can identify focal lymphatic malformations, thoracic lymphangiectasia or lymphangiomatosis, but distinguishing lymphatic fluid from non-lymphatic effusions is difficult. Abdominal and pelvic CT scans obtained with oral and intravenous contrast enhancement may demonstrate diffuse, nodular, small bowel wall-thickening and edema.[4] Chylous ascites may demonstrate a unique biphasic fat-fluid level when the patient to positioned lying flat.[9]
Conventional Intranodal Lymphangiography: Percutaneous canulation of groin lymph nodes followed by injection of an oil-based iodinated contrast agent allows for imaging of the central conducting lymphatic vessels with adequate characterization of patterns of lymphatic flow.[10] Compared to historic use of pedal lymphangiography, direct contrast injection into lymph nodes of the groin has a higher success rate to produce informative diagnostic imaging of abdominal and thoracic lymphatics. Although modern interventional practices have shortened procedure time and decreased cumulative fluoroscopy exposure, anesthesia is required for pediatric patients and should be discussed when reviewing the risks and benefits of pursuing lymphangiography. Conventional intranodal lymphangiography is contraindicated in patients with a known right to left cardiac shunt given the potential stroke risk.
Non-contrast Magnetic Resonance Lymphangiography: Static T2 weighted non-contrast MR lymphangiography has a high sensitivity and specificity to demonstrate abnormal lymph vessels and abnormal draining patterns in the peripheral lymphatic system.[11] Non-contrast MR lymphangiography can image both central and peripheral lymphatic systems but is a static image with no data to characterize lymphatic flow. Magnetic resonance imaging (MRI) reduces ionizing radiation exposure but may require sedation for prolonged studies.
Dynamic Contrast-Enhanced MR Lymphangiography (DCMRL): DCMRL is the current imaging modality of choice to image the central lymphatic system, identify lymphatic leaks and plan interventional or surgical procedures.[10] However, the availability of DCMRL can vary nationally and success of imaging can be operator dependent. The technique has several advantages over conventional fluoroscopic lymphangiography including that it is 3D, has good distal distribution of contrast, and has good tissue contrast. Intranodal DCMRL (IN-DCMRL) involves ultrasound guided groin lymph node access followed by injection of a gadolinium contrast agent into the lymph node and then dynamic and static contrast enhanced MRI imaging of the abdomen and thorax.[12, 13] This technique is good for imaging the central lymphatic system including the cysterna chyli and thoracic duct (TD) and is the default imaging modality for pulmonary lymphatic disorders that are often supplied by fluid that originates from the TD (Figure 2a) . IN-DCMRL allows for evaluation of the central lymphatic system prior to interventions or surgery; however, the two main contributors to central lymphatic flow, the liver and the mesentery, which play a key role in several disease processes such as protein losing enteropathy (PLE) and ascites, are not often imaged with IN-DCMRL. Recently, intrahepatic (IH) and intramesenteric (IM) DCMRL allow imaging of these two important lymphatic streams.[14, 15] Intrahepatic and intramesenteric DCMRLs are the imaging modalities of choice for imaging abdominal lymphatic abnormalities such as PLE and ascites and should be used in conjunction with IN-DCMRL in cases with multicompartment lymphatic disorders to better characterize the extent of the lymphatic abnormality and to plan treatments (Figure 2b, 2c).